Cold Email Inbox Calculator — How Many Inboxes Do I Need?
Calculate exactly how many inboxes and domains you need for your cold email volume. Enter your daily send target and get inbox count, domain count, rotation strategy, and cost estimate for Google Workspace and Outlook 365.
How It Works
- Google Workspace — 15 cold emails per inbox per day. Higher per-inbox cost but fewer inboxes needed.
- Outlook 365 — 3 cold emails per inbox per day. Lower per-inbox cost but more inboxes required.
- 3 inboxes per domain — Industry standard. Limits blast radius if one inbox gets flagged.
Common Setups
| Daily Volume | Google Inboxes | Outlook Inboxes | Google Domains | Outlook Domains |
|---|---|---|---|---|
| 50/day | 6 | 51 | 2 | 17 |
| 100/day | 9 | 102 | 3 | 34 |
| 500/day | 36 | 501 | 12 | 167 |
| 1,000/day | 69 | 1,002 | 23 | 334 |
Rotation Best Practices
- Never put more than 3 inboxes on a single domain
- Never send cold email from your primary business domain
- Space sends 5-15 minutes apart for Google, 15-30 minutes for Outlook
- Round-robin across all inboxes — don't burst from a single one
- New inboxes need 2-3 weeks of warmup, or use pre-warmed inboxes to skip this